Simple headlights in the automotive field presently offer the selection between multiple fixedly defined light distributions, for example, low beams, high beams, and fog lights.
So-called “adaptive” headlight systems having variable light distributions supplement this selection and offer, for example, dynamic cornering lights, freeway, city, and bad weather lights. The selection of the light distributions is partially performed depending on the situation by the headlight system and/or the central electronics of the vehicle.
So-called “active” headlights also exist in the field of vehicle illumination, in which a limited number of pixels arranged in columns can be generated. Using active headlights it is possible, for example, to mask oncoming and leading vehicles within their own high beam cone (“dazzle-free high beams”) or to emphasize sources of risk by direct illumination for the driver. One possible technical implementation of an active headlight is based on a luminophore which can be excited by means of laser radiation. The luminophore is “scanned” in this case using the exciting radiation and then imaged with the aid of a projection optical unit. The principle is described, for example, in the documents DE 10 2010 028 949 A1, US 2014/0029282 A1, and WO 2014/121314 A1. These documents describe that dynamically adaptable light distributions are generated on the luminophore in that the laser radiation used for exciting the luminophore is regulated with the aid of a controllable light deflection unit in the form of a movable micromirror. A desired light distribution can be achieved in this case (as described in US 2014/0029282 A1), via an intensity modulation of the laser source, via an adaptation of the angular velocity of the deflection unit, and also via a combination of both mechanisms.
The luminophores necessary for the wavelength conversion or conversion of the laser light are limited because of the so-called “thermal quenching” with respect to the conversion rate thereof and/or a maximum acceptable power density (for example, because of the physical material properties thereof such as a resistance to “laser ablation”) and therefore are limited with respect to the maximum luminance thereof. This limit of the luminance limits the resulting luminous flux per cross-sectional area of the luminophore element illuminated (by the laser beam). To achieve the luminous flux required for a headlight, for example, a minimum illuminated area on the luminophore element and therefore a minimum cross-sectional area of the laser beam is therefore necessary. While the luminous flux increases with increasing beam diameter (with constant power density of the beam), the achievable resolution decreases. A goal conflict thus exists between the resolution and the achievable luminous flux. An increase of the resolution causes a reduction of the luminous flux per pixel and vice versa. The only possibility for avoiding the negative consequences of the luminance limiting of the luminophore, without reducing the resolution, is to distribute the luminous flux onto multiple laser beams. The technical implementations thereof have the disadvantage that they result in a high alignment expenditure and require a large amount of installation space for the arrangement of the light sources and/or the deflection units.